CARBONATE OF POTASH. 



is afterwards filtered. This solution gives crystals of sulpho- 

 cyanide of potassium, when evaporated, which may be freed 

 from any adhering carbonate of potash, by dissolving them in 

 alcohol. The salt crystallizes in long white striated prisms, 

 which are anhydrous, and resemble nitrate of potash in their 

 appearance and taste. They deliquesce in a damp atmosphere, 

 and are very soluble in hot alcohol, from which the salt 

 crystallizes on cooling. The sulphocyanide of potassium com- 

 municates a blood red colour to solutions of salts of perox- 

 ide of iron, and is consequently employed as a test of that 

 metal in its higher state of oxidation. The red solution is 

 made perfectly colourless by a moderate dilution with water, 

 when the iron is not present in excess. The sulphocyanide of 

 potassium has been detected in the saliva of man and the sheep. 



SALTS OF POTASH. 



Carbonate of potash ; KO, CO 2 ; S66.3 or 69.42. This use- 

 ful salt is principally obtained from the ashes of plants. Potash 

 is always contained in a state of combination in clay and other 

 minerals which form the earthy part of soil, and appears to be a 

 constituent of soil essential to vegetation. The alkali is appro- 

 priated by plants, and is found in their sap combined with vege- 

 table acids, particularly with oxalic and tartaric acids ; also with 

 silicic and sulphuric acids, and as chloride of potassium. When 

 the plants are dried and burned, the salts of the vegetable acids 

 are destroyed, and leave carbonate of potash ; shrubs yielding 

 three, and herbs five times as much saline matter as trees ; and 

 the branches of trees being more productive than their trunks, 

 a distribution which may depend upon the potash existing 

 chiefly in the sap. The whole ashes from wood seldom exceed 

 1 per cent of its weight, of which l-6th may be saline matter. 

 The solution evaporated to dryness yields Potashes, and these 

 partially purified and ignited form Peai lash. The carbonate is 

 mixed in the latter with about 20 per cent of foreign salts, 

 principally sulphate of potash and chloride of potassium. The 

 carbonate of potash is obtained in a state of greater purity by 

 dissolving pearlash in an equal weight of water, then separating 

 the solution from undissolved salts, and evaporating it to 

 dryness. 



Carbonate of potash is prepared of greater purity for chemical 



